Reactions of divalent transition metal halides with 3,5-dimethyl-1- (hydroxymethyl)-pyrazole: Part 23. Transition metal complexes with pyrazole-based ligands

Article abstract of DOI:10.1007/s10973-006-7564-8

Factors determining the complex formation reaction of copper(II), nickel(II) and cobalt(II) chloride and copper(II) bromide with 3,5-dimethyl-1-(hydroxymethyl)-pyrazole (HL) has been studied. Depending on experimental conditions, complexes with different

Full text of DOI:10.1007/s10973-006-7564-8

Journal of Thermal Analysis and Calorimetry, Vol. 89 (2007) 1, 267–275
REACTIONS OF DIVALENT TRANSITION METAL HALIDES WITH
3,5-DIMETHYL-1-(HYDROXYMETHYL)-PYRAZOLE
Part 23. Transition metal complexes with pyrazole-based ligands
1
V. M. Leovac , R. Petkoviº , A. Kovács , G. Pokol and Katalin Mészáros Szécsényi
1
2
3
1*
1
University of Novi Sad, Faculty of Sciences, Department of Chemistry, 21000 Novi Sad, Trg D. Obradoviºa 3
Serbia and Montenegro
2
Hungarian Academy of Sciences, Budapest University of Technology and Economics, Research Group of Technical Analytical
Chemistry, 1111 Budapest, Szt. Gellért tér 4, Hungary
Institute for General and Analytical Chemistry, Budapest University of Technology and Economics, 1521 Budapest
3
Szt. Gellért tér 4, Hungary
Factors determining the complex formation reaction of copper(II), nickel(II) and cobalt(II) chloride and copper(II) bromide with
3
,5-dimethyl-1-(hydroxymethyl)-pyrazole (HL) has been studied. Depending on experimental conditions, complexes with different com-
position were obtained: [CuCl (dmp)] (I), [CuCl (dmp) (II), [CoCl (dmp) ] (III) (dmp=3,5-dimethylpyrazole), [CuBr(L)] (IV),
CoCl(L)(EtOH)] (V) and [NiCl(L)(EtOH)] (VI). The compounds were characterized by FTIR spectroscopy, solution conductivity and
magnetic measurements. The crystal structure of [CoCl(L)(EtOH)] has been determined by single crystal X-ray diffraction. The thermal
decomposition of the compounds was studied and found to be continuous for all of the compounds. The desolvation mechanism of
MCl(L)(EtOH)] (M=Co(II), Ni(II)) is explained on the basis of the route of complex formation of CoCl with HL.
2
2
2
2 2
]
2
2
2
[
4
4
4
[
4
2
Keywords: cobalt(II)-, copper(II)- and nickel(II) chloride and bromide complexes, 3,5-dimethyl-1-(hydroxymethyl)-pyrazole,
,5-dimethylpyrazole, FTIR, TG, XRD
3
Introduction
influence of various subsituents, changing them one
by one. Besides, we are investigating how the struc-
ture of the compounds affects the course of their ther-
mal decomposition. Special attention is paid to deter-
mine the structural characteristics of complexes
whose thermal decomposition results in formation of
relatively stable intermediates. The acquired knowl-
edge of factors governing the course of the reaction
and the thermal decomposition may serve to predict
the experimental conditions for formation of com-
pounds with a proposed composition.
In this paper we report the complex formation of
copper(II), nickel(II) and cobalt(II) chloride and cop-
per(II) bromide with 3,5-dimethyl-1-(hydroxy-
methyl)-pyrazole (HL) and selected physico-chemical
properties of the formed compounds. As the 1-N-hydro-
xymethyl-group may be a subject of deprotonation, the
role of base (KOH) in the course of the complex forma-
tion was also examined. The thermal decomposition of
the compounds was determined by TG and DSC. From
The resemblance of pyrazoles to imidazole deriva-
tives as regular constituents of proteins makes the
pyrazole based ligands as well as their complexes an
attractive research area [1–5]. Complexes with
pyrazole derivatives are often used to mimic enzy-
matic reactions which are very selective and con-
ducted under mild conditions. Due to these character-
istics of pyrazole complexes, there are attempts to test
their catalytic activity to obtain specific industrial
polymeric products [6]. One of their application fields
includes thin film processing by metal organic chemi-
cal vapor deposition processes (MOCVD) [7–9]
which claims for examining the thermal behavior of
potential precursors including coupled TG-MS or
TG-IR methods [10–16].
Our systematic studies on complexes with
pyrazole based ligands aim to determine the key fac-
tors controlling the course of the complex forma-
tion [17–21]. The primary coordination site of
pyrazole is its pyridine nitrogen atom, N(2). Depend-
ing on the nature and the position of the ring substitu-
ents, the number of coordination sites may be in-
creased [22–24]. One of our main goals is to track the
the obtained complexes [CuCl (dmp)]2
(I),
[CuCl (dmp) ] (II), [CoCl (dmp) ] (III) (dmp=3,5-di-
2
2
2 2
2
2
methylpyrazole),
[NiCl(L)(EtOH)] (VI) [18, 25–27] are already known
[CoCl(L)(EtOH)]4
(V)
and
4
in the literature. The only novel complex obtained in the
*
Author for correspondence: mszk@uns.ns.ac.yu
1
388–6150/$20.00
Akadémiai Kiadó, Budapest, Hungary
Springer, Dordrecht, The Netherlands
©
2007 Akadémiai Kiadó, Budapest

LEOVAC et al.
present study is [CuBr(L)] (IV). However, the previous
2
green precipitate. It was filtered off after 24 h, washed
with cold EtOH and dried at room temperature. Yield:
88.7%. Elemental analysis data, Found% (Calcd.%):
C, 21.74 (20.62); H, 2.77 (2.88); N, 8.38 (8.02),
synthesis of the compounds was carried out under dif-
ferent conditions. Thus, reporting their synthesis gives
contribution to understand the controlling factors of
complex formation reactions. The thermal decomposi-
tion of (I), (II) and (III) has also been reported [18]
while for the other compounds it is determined here for
the first time.
2
–1
l
M
=31.6 S cm mol , meff =1.46 m
that the elemental analysis data and TG curves refer to
a compound with a composition of [CuBr (HL)] and
B
. In spite of the fact
2
2
the powder X-ray data suggest a different compound
than that forming in the presence of KOH in a
salt-to-ligand ratio of 1:2, the complex formation was
not reproducible enough and a detailed discussion on
this compound is omitted in this paper.)
Experimental
CoCl
1 mmol in 5 cm EtOH) with HL (1 mmol in
(dmp) , III: In reactions of CoCl ×6H O
2 2 2 2
Materials
3
(
2.5 cm EtOH) in 1:1 and 1:2 mole ratio (2 mmol HL
3
Reagents
3
in 5 cm EtOH) a blue 3,5-dimethylpyrazole complex,
All chemicals were analytical grade commercially
available products.
CoCl (dmp) , was obtained. The mixture was kept at
2
2
room temperature for 5 h. The precipitate was filtered,
washed with cold EtOH and air dried. The crystal
structure of the compound is identical to that deter-
mined by Oki et al. [26]. Yield: about 20%. Found%
Syntheses
All the reactions were carried out with crystal hydrates
of the corresponding metal salts in ethanolic solutions.
(
(
Calcd.%): C, 36.94 (37.29); H, 5.11 (5.01); N, 16.84
–1
2
17.39). l
=28.2 S cm mol .
M
[
On mixing of solutions of CuCl (2 mmol, in 13 cm
CuCl (dmp)] , I (dmp=3,5-dimethylpyrazole):
2 2
3
[CoCl(L)(EtOH)] , V: The above described reac-
4
2
3
EtOH) and HL (0.24 g, 2 mmol, in 7 cm EtOH) an
tion was repeated in a salt-to-ligand mole ratio of 1:2
1 mmol CoCl ×6H O and 2 mmol of HL in EtOH, total
(
2
2
immediate precipitation was observed. The yellow
microcrystalline product I, was filtered off after 3 h,
washed with cold ethanol and air dried. Yield: 52.0%.
Found% (Calcd.%): C, 26.06 (26.04); H, 3.49 (3.56);
3
volume of 10 cm ) under reflux for 3 h. During a 12 h
stay the same blue single crystals of III were formed,
contaminated with crystals of V which were mechani-
cally removed. The mother liquid was placed in a deep
freezer. After 48 h deep purple single crystals of
–
1
N, 12.00 (12.15). FTIR spectrum (cm , KBr): 3338s,
1
1
571s, 1471m, 1413m, 1278s, 1184m, 1153m, 1049s,
2
–1
=36.0 S cm mol .
M
[
CoCl(L)(EtOH)]
filtered, washed with cold EtOH and air dried. The yield
was about 10% calculated on the basis of CoCl ×6H O.
4
were obtained. The precipitate was
028m, 792m, 569m. l
[
CuCl (dmp) ] , II: 24 h after the precipitation of
2
2 2
the mono(ligand) complex, I, green single crystals
of II were obtained from the green colored filtrate.
The crystals were washed with cold EtOH and dried
on air. Yield: 6.1%. Found% (Calcd.%): C, 36.48
(36.76); H, 4.70 (4.94); N, 19.96 (17.15). FTIR spec-
1
trum (cm , KBr): 3268s, 3203s, 3148m, 1571s,
2
2
When the reaction was carried out by mixing of cold
about 5°C) ethanolic solutions of the ligand and CoCl
and the mixture was kept in a deep freezer (at about
15°C) for 48 h, only the purple crystals of V were ob-
(
2
–
–
tained, but the yield was even lower than in the former
case. Found% (Calcd.%): C, 36.0 (36.18), H, 5.6 (5.69),
1
1
6
493m, 1472m, 1413m, 1275m, 1183m, 1171m,
145m, 1050m, 1043m, 819m, 795m, 701m, 687m,
2
–1
N, 10.6 (10.55), l
=54.2 S cm mol .
M
2
–1
=30.6 S cm mol .
[NiCl(L)(EtOH)] , VI: NiCl ×6H O and HL were
reacted in a salt-to-ligand mole ratio of 1:1 (1:1 mmol,
14m. l
M
4
2
2
[
cm EtOH with 10 drops of 10% KOH and
CuBr(L)] , IV: Solutions of 2 mmol of HL in
3
2
3
total volume: 7.5 cm ) and 1:2 (1:2 mmol, total vol-
6
1
3
ume: 10 cm ) at room temperature. The reactions were
3
mmol CuBr in 6 cm of EtOH were mixed. Precipi-
2
3
carried out also in the presence of 5 drops (»0.2 cm ) of
tation followed immediately which was dissolved in a
boiling solution. The clean solution was left to cool to
room temperature. The green precipitate was filtered
off after 24 h, washed with cold EtOH and air dried.
Yield: 52%. Found% (Calcd.%): C, 26.70 (26.83);
10% KOH. In all the cases the same green single crys-
tals of [NiCl(L)(EtOH)]4 were formed, with a
cubane-type structure determined previously by X-ray
diffraction by Paap et al. [27]. Yield: about 25% in all
–1
four procedures. FTIR spectrum (cm , KBr): 3414s,
H,
l
3.34
=39.4 S cm mol , meff =1.66 mB. (The reaction of
M
(3.38);
N%:
10.10
(10.43).
2
–1
2
1
924m, 2887m, 1553vs, 1463s, 1423s, 1386s, 1257s,
145m, 1101vs, 1051vs, 842s, 775s, 684s. Found%
CuBr with L has also been carried out without KOH.
2
3
Mixing of 20 cm solution containing 2 mmol CuBr
(
(
Calcd.%): C, 34.78 (36.21); H, 5.41 (5.70); N, 10.29
2
2
–1
3
with 20 cm solution of 2 mmol L, resulted in light
10.56). l =69.5 S cm mol .
M
268
J. Therm. Anal. Cal., 89, 2007

REACTIONS OF DIVALENT TRANSITION METAL HALIDES
Methods
Elemental analysis (C,H,N) was performed by stan-
dard methods.
A single crystal of V with approximate dimensions
3
of 0.08×0.08×0.12 mm was selected for data collection.
The X-ray structure data were collected on a
Bruker AXS SMART diffractometer with an
APEX CCD detector, equipped with a Bede Micro-
Scheme 1
Ò
source X-ray generator, using MoK
radiation. A full
a
preparation. With Cu(NO
[
3
)
2
a
Cu(dmp) (NO ) ] was obtained, i.e., the same kind of
mononuclear
sphere of data was collected with a frame width of 0.3°
and a counting time of 20 s per frame. A multiscan ab-
sorption correction [28] was applied to the raw data
and the resulting Rint was 3.2%. Frames were inte-
grated using the program SAINT [29]. The crystal
structure was solved by direct methods using the
SIR92 software [30] and refined using the Oxford
Crystals suite [31]. The positions and atomic displace-
ment parameters of all non-hydrogen atoms were re-
fined; hydrogen atoms were located from difference
Fourier maps and refined isotropically using restraints.
FTIR spectra were recorded at room temperature
3
3 2
splitting of the ligand was observed. In pure
propan-2-ol Cu(II) salts gave binuclear complexes
[
Cu(dmp)(L)X] (X=NO , BF , ClO ), which means
2 3 4 4
that only one ligand had lost HCOH, while the other
ligand molecule coordinated in its deprotonated form.
Splitting of the 1-N-substituent was also observed in
the reaction of CuCl with 1-carboxamide- 3,5-di-
2
methylpyrazole, (L1, Scheme 2), [18]. The explanation
of the phenomenon may partly be based on the HSAB
principles [34–36] of binding preferences of the me-
dium soft Cu(II) acid to the medium soft pyridine nitro-
gen (Npy) of the ring, taking into account the favorable
steric effects caused by departing of the 1-N
–
1
using KBr pellets in the range of 4000–450 cm on a
PerkinElmer System 2000 FTIR spectrometer with
MCT detector and co-addition of 16 scans. The far-IR
substituent. In reaction of copper(II) chloride with
1
-(2-hydroxyethyl)-pyrazole (HL ) in ethanolic solu-
–
1
(
polyethylene pellets and DTGS detector. The spectra
650–150 cm ) measurements were carried out with
1
tion no splitting of the 1-N-substituent was observed,
–
1
were obtained with a resolution of 4 cm .
Magnetic susceptibility measurements were con-
ducted at room temperature on an MSB-MKI mag-
netic susceptibility balance Sherwood Scientific Ltd.,
Cambridge.
instead, a spontaneous deprotonation of the ligand took
was obtained [37]. Under similar
experimental conditions with 3,5-dimethyl-1-thio-
carboxamidepyrazole, (L2, Scheme 2) the ligand coor-
dinated to the metal forming a neutral centrosymmetric
1
place and [Cu(L )X]
2
Molar conductivity of freshly prepared
–3
mol dm solutions in DMF was measured at
[Cu(L2)Cl ] complex [38].
2 2
–
3
1
0
The mechanisms of reactions of CuBr with L1
2
room temperature using a digital conductivity meter
Jenway 4010.
and L2 are different. In the reaction of CuBr with
2
1-carboxamide-3,5-dimethylpyrazole (L1), one ligand
Thermal analysis was performed using
DuPont 1090 TA system with sample masses of about
mg. In the thermogravimetric measurements platinum
a
molecule undergoes decarboxamidation [19] together
with spontaneous deprotonation of the other ligand’s
carboxamide group. The binding preferences deter-
mined by the HSAB principle still hold in this mole-
cule, but in addition, one voluminous bromide ion is
replaced with the deprotonated ligand, via NH of the
carboxamide group, reducing thus the steric repulsion
5
crucible was employed, while the DSC curves were re-
corded up to 600 K using an open aluminum pan sample
holder with an empty aluminum pan as reference. The
measurements were carried out in both argon and air at-
–1
mospheres at a heating rate of 10 K min .
Results and discussion
In the reaction of HL with CuCl the splitting of the
2
1
formation of two dmp complexes, [CuCl (dmp)] and
-hydroxymethyl substituent occurs, leading to the
2
2
[
CuCl (dmp) ] (Scheme 1).
2 2 2
Barszcz et al. also investigated the complex for-
mation reactions of copper(II) salts with HL [32, 33]
depending on the solvent (mixtures of trimethyl
orthoformate, methanol and propan-2-ol) used in the
Scheme 2
J. Therm. Anal. Cal., 89, 2007
269

LEOVAC et al.
inside the [CuBr(dmp)(L1)] molecule. During the
2
of the ligand occurs only when the CuBr to HL ratio
2
complex formation of CuBr2 with 3,5-dimethyl-
1-thiocarboxamide-pyrazole, (L2), Cu(II) is reduced to
Cu(I), [38] leading to the same effect: the molecule
contains only one bromide per copper(I) resulting in
is 1:2. The salt-to-ligand ratio has no significant ef-
fect in reactions of NiCl ×6H O and CoCl ×6H O with
HL. Our finding is that the reaction of NiCl with HL
is not affected by the presence or absence of the base:
under all examined reaction conditions the only prod-
ucts are single crystals of VI, prepared by Paap et al.
[26], in the presence of KOH. This means a spontane-
ous ligand deprotonation with nickel(II) chloride.
2
2
2
2
2
reduced steric repulsion in [Cu Br (L2) ]. In addition,
2 2 2
in the later complex the soft–soft interactions are domi-
nant, except of that with the pyrazole N, which belongs
to medium soft bases. In IV, with soft bromide bridges,
the steric repulsions decrease, due to the deprotonation
In the reaction of CoCl with HL, in the presence
2
of CH OH-group in the presence of KOH. The binding
2
of KOH, III was formed as the main product, i.e., the
1-N-substituent of the ligand had split, as with CuCl2.
From the mother liquid V was formed at low tempera-
ture in a deep freezer. The quality of the crystals al-
lowed the crystal structure determination. The crystal
data are presented in Table 1, while selected bond
lengths and angles are given in Table 2. The molecu-
lar diagram and the atom numbering scheme of V is
presented in Fig. 1 while a view of its packing is
shown in Fig. 2. In the crystal, the chlorine atoms are
preferences in the compound, according to the HSAB
principles, between the medium soft Cu(II) acid, the
medium soft pyrazole N and the somewhat harder
deprotonated –CH OH bases are still in the acceptable
2
range, so neither the reduction of Cu(II) nor the split-
ting of N-substituent is taking place.
It is often found that the ligand anion formed by
deprotonation replaces the counterion of the metal salt.
Steric repulsions in such a molecule are usually reduced
and, as a consequence, more stable compounds may
form. In order to examine how the presence of a base af-
fects the deprotonation of the ligand and the complex
formation, the reactions with CuBr , NiCl and CoCl
2 2 2
were carried out both with and without KOH.
In the reaction of CuBr with 3,5-dimethyl-
2
1
-(hydroxymethyl)-pyrazole (HL) the deprotonation
Table 1 Crystal data of [CoCl(L)(EtOH)]
Chemical formula
4
C
32
H
60Cl
4
Co
1062.42
monoclinic
P2 /n
4 8 8
N O
Molecular mass/amu
Crystal system
Space group
1
a/
b/
c/
a/°
b/°
g/°
13.3604(13)
17.6288(18)
20.268(2)
90
Fig. 1 The molecular diagram and the atom numbering
107.704(2)
90
4
scheme of [CoCl(L)(EtOH)] . Atomic displacement pa-
rameters are given at 50% probability level. Hydrogen
atoms have been omitted for clarity
3
V/
4547.7(8)
4
Z
T/K
120
–
3
Calculated density/g cm
–
m/mm
1.552
1
1.722
Total number of reflections
Number of unique reflections
Number of observed reflections
53721
13230
8
310
(
I>2s)
Number of parameters refined
745
3.50
3.04
9.11
R
int /%
R/% for I>2s
wR/% for all reflections
Fig. 2 Packing diagram for [CoCl(L)(EtOH)]
4
270
J. Therm. Anal. Cal., 89, 2007

REACTIONS OF DIVALENT TRANSITION METAL HALIDES
Table 2 Selected bond lengths () and angles (°) of [CoCl(L)(EtOH)]
4
Length
Length
Co(1)–O(9)
Co(1)–Cl(5)
2.3722(8)
2.135(2)
2.0984(19)
2.124(2)
2.142(2)
2.1369(18)
2.117(2)
2.1227(18)
1.429(3)
1.437(4)
1.346(4)
1.355(3)
1.483(4)
1.351(4)
2.1189(19)
2.1118(18)
2.120(2)
2.149(2)
2.108(2)
2.122(2)
1.375(3)
1.415(4)
1.366(3)
1.366(3)
1.365(3)
1.342(4)
Co(1)–O(16)
Co(1)–N(20)
Co(2)–O(11)
2.1177(18)
2.3710(8)
2.1079(18)
2.1118(18)
1.400(3)
Co(2)–O(13)
Co(3)–Cl(8)
Co(3)–O(9)
Co(3)–O(15)
Co(3)–N(24)
Co(4)–O(11)
Co(4)–O(12)
O(9)–C(26)
O(10)–C(27)
O(13)–C(36)
1.442(3)
O(14)–C(33)
N(17)–N(19)
1.369(3)
N(17)–C(42)
N(18)–C(26)
1.467(4)
N(18)–C(39)
N(20)–C(32)
1.343(4)
N(21)–C(38)
N(22)–C(51)
1.474(3)
N(22)–C(54)
Co(1)–O(11)
2.1414(18)
2.3676(8)
2.1464(19)
2.1287(19)
2.3761(8)
2.1094(19)
1.385(3)
Co(1)–O(12)
Co(2)–Cl(6)
Co(2)–O(9)
Co(2)–O(15)
Co(2)–N(23)
Co(3)–O(12)
Co(3)–O(14)
Co(4)–Cl(7)
Co(4)–O(10)
Co(4)–O(15)
Co(4)–N(19)
O(11)–C(45)
O(12)–C(38)
O(15)–C(51)
1.381(3)
O(16)–C(37)
N(17)–C(45)
1.478(3)
N(18)–N(23)
N(19)–C(28)
1.339(3)
N(20)–N(21)
N(21)–C(48)
1.351(4)
N(22)–N(24)
N(23)–C(25)
1.331(4)
N(24)–C(40)
Angle
Angle
Cl(5)–Co(1)–O(9)
Cl(5)–Co(1)–O(16)
O(9)–Co(1)–O(12)
O(11)–Co(1)–O(12)
O(12)–Co(1)–O(16)
Cl(6)–Co(2)–O(9)
Cl(6)–Co(2)–O(15)
O(9)–Co(2)–O(13)
Cl(5)–Co(1)–O(12)
O(9)–Co(1)–O(11)
O(9)–Co(1)–N(20)
O(11)–Co(1)–N(20)
100.68(5)
Cl(5)–Co(1)–O(11)
Cl(5)–Co(1)–N(20)
O(9)–Co(1)–O(16)
O(11)–Co(1)–O(16)
O(12)–Co(1)–N(20)
Cl(6)–Co(2)–O(11)
Cl(6)–Co(2)–N(23)
O(9)–Co(2)–O(15)
O(16)–Co(1)–N(20)
Cl(6)–Co(2)–O(13)
O(9)–Co(2)–O(11)
92.80(5)
102.93(7)
84.99(8)
163.42(8)
77.04(8)
99.23(5)
104.09(6)
79.11(7)
82.70(9)
92.29(6)
79.89(7)
96.19(7)
80.93(7)
79.94(7)
91.55(8)
173.33(5)
94.23(5)
94.25(7)
172.21(5)
79.65(7)
154.37(8)
108.85(8)
connected to the ethanolic OH groups by intra-
molecular hydrogen bonds.
tion and structure were proposed on the basis of ele-
mental analysis data and FTIR spectroscopy. The
band assignment is given in Table 3, together with a
detailed IR-spectral analysis of V and III. The assign-
ment was primarily based on quantum chemical com-
putations on HL at the B3LYP/6-311++G** level and
on dmp and [CuBr(L)] at the B3LYP/6-31G** level
2
using an effective core potential for Cu [39]. The
spectral characterization of the other investigated
The crystal structures of II and III have already
been reported ([25, 26], respectively). However, we
have checked their thermal decomposition in order to
see how the route of the complex formation affects
the decomposition pattern of the compounds. As the
new copper(II) bromide complex, IV, could not be
obtained in the form of single crystals, its composi-
J. Therm. Anal. Cal., 89, 2007
271

LEOVAC et al.
a
4 2 2 2
Table 3 Characteristic bands in the FTIR spectra of [CoCl(L)(EtOH)] , CoCl (dmp) and [CuBr(L)]
b
[
CoCl(L)(EtOH)]
4
CoCl
2
(dmp)
2
[CuBr(L)]
2
Assignment
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
3345s
n
n
N–H
N–H
3313s
2978m
2926m
2888m
2879sh
1552vs
1479sh
1463s
1422s
1386s
1378sh
1260s
1163m
1147m
1096vs
1047vs
985m
2963w
2924m
2869vw
2841vw
1569vs
2958m
2926m
2882m
2868m
1548s
nas(CH3 )
nas(CH3 )
ns(CH3 )
ns(CH3 )
n
ring
1482m
1462s
sci CH
2
1470s
1406s
1378m
n
n
ring, das(CH3 )
ring, das(CH3 )
ds(CH3 )
1
1
1
1
1
1
1
1
1
1
2
2
2
2
1420m
1389m
1370s
wag CH
2
1271s
1165s
1148s
1099m
1049vs
983w
1245s
nring, n(N– CH2 )
d
ring
ring
1148s
1089vs
1057s
991sh
845m
777m
699s
d
n
C–O, das(CH3 )
d
ring
rock CH
3
839s
n(N– CH2 )
774s
819s
wagC–Hring
684s
703s
t
t
d
ring
ring
ring
629m
660m
586m
626w
571w
597vw
4
27m
wagN–H
a
The abbreviations vs, s, m, w, vw and sh mean very strong, strong, medium, weak, very weak and shoulder, respectively.
b
Main components of the fundamentals. The symbols n, d and t indicate stretching, deformation and torsion vibrations, respectively,
while the abbreviations s, as, sci, wag and rock mean symmetric, asymmetric, scissoring, wagging and rocking, respectively
compounds is not given, only the characteristic bands
are listed in the ‘Experimental’.
ture Database confirmed that the arrangement of lig-
ands around Cu(II) for tetracoordinated complexes is
generally distorted square planar (Scheme 3).
The positions of the n
bands in III at 340
ones at 235
Co–Cl
–
and 308 cm , as well as those of the n
1
Co–N
The molar conductivity data in DMF refer to the
non-electrolyte character of all the compounds except
the isomorphous cuban-type Ni(II), VI, and Co(II), V,
complexes. The value of the molar conductivity of VI
belongs to an electrolyte of 1:1 type, referring to a
complete exchange of one chloride ion with DMF,
while in V the conductivity is somewhat less than that
corresponding to 1:1 electrolytes.
–
1
and 200 cm are characteristic for tetrahedral coordi-
nation around Co(II) [40] in CoCl (dmp) , as was also
found by single crystal structure determination [26].
2
2
For the novel [CuBr(L)] complex the good
2
agreement between the computed and experimental
IR spectra supports the proposed structure presented
in Scheme 3. The strong band in the far IR region at
–
1
3
98 cm is assigned to nCu–O on the basis of previous
observations on related compound [33] supported
also by the computations, while the nCu–N, nCu–Br and
dCu–O vibrations appear superimposed in a broad band
–
1
in the 170–300 cm region. The computations re-
sulted in a distorted square-planar arrangement
around the Cu atoms in the equilibrium structure of
[
CuBr(L)]
magnetic moment relative to the spin-only value
m =1.66 m ) supports also the binuclear character of
2
(cf. Scheme 3). The lower value of the
(
eff
B
Scheme 3
the complex [41]. Our search of the Cambridge Struc-
272
J. Therm. Anal. Cal., 89, 2007

REACTIONS OF DIVALENT TRANSITION METAL HALIDES
Thermal decomposition of the compounds
The IR-spectrum of an isolated degradation product of
blue color at 580 K (about 20% mass loss) refers to the
formation of III. However, the decomposition product
is not stable (the decomposition of III begins at about
The thermal decomposition of the reaction products of
CuCl with HL has been published recently [18]. Re-
2
peating the thermal analysis in the present study we ob-
tained slightly different decomposition patterns due to
the different structural characteristics, as a result of the
different experimental conditions in the two studies.
This is not an unknown phenomenon. The topology in
chemistry refers to the so-called memory effect which
means that compounds ‘remember’ the conditions un-
der which they were produced [42]. In contrast to the
1
00 K lower temperature). The band assigned to nring
–1
and nN–CH2 vibrations of III at 1271 cm is present in
the IR spectrum of the decomposition product, but with
significantly lower relative intensity than found in the
spectrum of III. Also the pyrrole nN–H vibrations of the
–1
dmp ligand show up at 3343 and 3340 cm . The end
products in air are most probably metal oxides (NiO,
%, found: 29.0, calcd: 28.15; CoO, %, found: 27.0%,
decomposition of [CuCl
1
2
(dmp)]
2
obtained with
-carboxamide-3,5-dimethylpyrazole, where a rela-
calcd: 28.21). The different desolvation mechanisms
may originate from the preferences of the complex for-
tively stable intermediate forms, the decomposition of
the complexes obtained with 3,5-dimethyl-1-(hydroxy-
methyl)-pyrazole is continuous in the whole tempera-
mation of CoCl with HL: the main product of the reac-
2
tion is III, while V is formed at low temperature in low
yield, so the thermal decomposition probably goes
through the formation of III, which is not stable at the
decomposition temperature of V.
It can not be excluded that the different desol-
vation mechanism of the latter two compounds may
be ascribed to the different distances between the cen-
tral Ni(II) and Co(II) atoms and the coordinating oxy-
gen atoms of EtOH molecules, presented in Table 4.
However, to support this preposition one has to com-
ture range. The decomposition of CoCl (dmp) , III,
2 2
with three clearly separated steps has a similar decom-
position pattern as the corresponding copper(II) chlo-
ride complex, II, in spite of the fact that the later com-
pound is a binuclear complex [25]. The thermal
stability of III is higher by about 30 K (470 K). The
composition of the end products of the decomposition
in air (>800 K) was calculated on the basis of the mass
losses. The percentage of the residue agree with pure
metal end products (Co, found: 17%, calcd: 18.30%,
Cu, found: 19%, calcd: 19.45%) and not CoCl for III,
2
as was found earlier [43]. (In our previous paper, [18],
the percentage of the residue was even less, 17%. Un-
fortunately, the calculated value was given as CuO, but
it was calculated for Cu. This means that the residue
should be Cu, consistent with the findings presented in
this paper. However, for an exact conclusion, the com-
position of the end products should be examined by
powder X-ray analysis.) The decomposition of the dmp
complexes in argon does not complete up to 1000 K.
The thermogravimetrical curves of the iso-
morphous cuban-type complexes, (V and VI) together
with the TG curves of the bromide complex, IV, are
presented in Fig. 3. All three compounds decompose
without forming stable intermediates. Even the
desolvated compounds could not be isolated.
The course of thermal decomposition of V and VI
does not depend on the atmosphere and, except that in
argon the decomposition is not completed up to
1
5
000 K. The thermal stability of VI is higher by about
0 K (400 K) compared to V. As the compounds are
isostructural, one would expect similar thermal decom-
position patterns. They are, however, different. The
desolvation of VI is a one-step process, loosing all four
EtOH molecules in a temperature range of less than
8
0 K. In V the evaporation of the two most loosely
bonded EtOH begins at 355 K and extends to about
0 K. At higher temperature the desolvation is accom-
7
Fig. 3 TG-DTG curves of complexes with HL, — – in argon,
-
panied with decomposition of the [CoCl(L)] moiety.
4
- - – in air
J. Therm. Anal. Cal., 89, 2007
273

LEOVAC et al.
Table 4 M–O(EtOH) distances in (V) and (VI) in *
mechanism in different atmospheres. In argon the su-
Co(1)–O(16)
Co(2)–O(13)
Co(3)–O(14)
Co(4)–O(10)
l(Co– O)(average)
2.135(2)
Ni(1)–O(9)
2.062(3)
2.070(3)
2.084(3)
2.084(3)
2.075 
0.022 
perimposing decomposition steps are better separated.
At about 650 K the DTG falls almost to zero and the
mass loss agrees to the formation of CuBr per mono-
mer unit (found, 45.2%; calcd: 46.59%). However, in
lack of TG-MS coupled measurement, this conclusion
is only optional. The decomposition is completed with
some coke residue around 1000 K. In air the end prod-
uct at 850 K is CuO (found: 30.6%, calcd: 29.61%).
The corresponding DSC curves (Fig. 4) show en-
dothermic decomposition for all three compounds.
Due to the beginning of the decomposition, the shape
of the curves does not refer to melting of the com-
pounds which was visually observed in the case of IV
and V. Complexes VI and III appear in form of grey-
ish green and black powder, respectively, after
desolvation. The evaporation steps of the first two
EtOH molecules in V complex are clearly separated
in the DSC diagram in accordance with the corre-
sponding DTG curve.
2.1420(19) Ni(2)–O(13)
2.1493(19) Ni(3)–O(15)
2.108(2)
2.133 
0.041 
Ni(4)–O(20)
l(Ni– O)(average)
D
max
D
max
*The Ni–O(EtOH) distances are determined under the
same conditions as the corresponding Co–O(EtOH)
distances. (DrCo(II)–Ni(II))=0.03 , [43])
pare the corresponding distances and the thermal de-
composition pattern for more isostructural solvates.
In addition, the thermal decomposition depends on
many, hardly controllable experimental conditions,
among others on the porosity of the samples, particle
sizes, etc. In order to check the reproducibility of the
TG measurement, the TG runs for these two samples
were repeated six times. The decomposition, within
the experimental uncertainty, was the same in all
measurements. However, to support the above propo-
sition, further coupled crystal structural and thermal
experimental data are needed.
Conclusions
The thermal decomposition of IV, [CuBr(L)] ,
2
shows a different course. In the absence of solvate mol-
ecules the decomposition temperature is somewhat
higher (420 K) compared with that of V and VI. In
contrast to the usual thermal behavior of similar com-
plexes where the decomposition pattern in argon does
not depend on the atmosphere up to about 600 K and
above this temperature the decomposition slows down,
the TG curves of IV suggest a different decomposition
CuCl forms two dmp complexes with HL as a conse-
2
quence of the splitting of the 1-N-hydroxymethyl
group. In the case of CuBr , NiCl and CoCl the com-
2
2
2
plex formation was studied in the presence of base
(KOH) and without it. It was found that the ligand
deprotonation is spontaneous with NiCl . In the reac-
2
tion with CoCl in basic solution two products were
2
obtained in the form of single crystals: CoCl (dmp)
2
2
is the primary product both at room temperature and
under reflux. The crystallization of [CoCl(EtOH)]4
takes place from the mother liquid in deep freezer.
When the reaction is carried out with cold solutions,
in deep freezer, the only product is [CoCl(EtOH)]4
with low yield. The crystal structure of this complex
was determined by X-ray diffraction. [CuBr(L)] was
2
obtained from basic solution with a 1:2 metal-to-
ligand ratio. Its structure was proposed on the basis of
elemental analysis data and IR spectral analysis. The
thermal decomposition of the compounds is continu-
ous. The different desolvation pattern of the isomor-
phous [MCl(EtOH)] complexes is most probably the
4
consequence of different complex formation prefer-
ence of CoCl with HL. The decomposition of all dis-
2
cussed complexes is endothermic in the whole inves-
tigated temperature range, accompanied with the
melting of IV and V.
Supplementary material
A full list of crystal data and refinement of V has been
deposited at the Cambridge Crystallographic Data
Centre, CCDC No. 604068.
Fig. 4 DSC curves of the complexes with HL
274
J. Therm. Anal. Cal., 89, 2007

REACTIONS OF DIVALENT TRANSITION METAL HALIDES
Acknowledgements
G. A. Bogdanoviº, ¦. K. Jaºimoviº and
A. Spasojeviº-de Biré, Inorg. Chim. Acta, 353 (2003) 251.
0 K. Howard, I. R. Evans, K. Mészáros Szécsényi,
V. M. Leovac and ¦. K. Jaºimoviº, J. Coord. Chem.,
57 (2004) 469.
2
The work was financed in part by the Ministry for Science and
Environmental Protection of the Republic of Serbia (Grant
o
N 142028) and Provincial Secretariat for Science and Tech-
nological Development of Vojvodina. Additional financial
support from the Hungarian Scientific Research Foundation
21 A. Kovács, D. Nemcsok, G. Pokol, K. Mészáros Szécsényi,
V. M. Leovac, ¦. K. Jaºimoviº, I. R. Evans, J. A. K. Howard,
Z. D. Tomiº and G. Giester, New J. Chem., 29 (2005) 833.
22 S. Trofimenko, Chem. Rev., 72 (1972) 447.
(
OTKA No. T038189) and computational time from the Na-
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Hungary is gratefully acknowledged. M. Sz. K. thanks the
Arany János and A. K. the Bolyai Foundation for support. The
authors would like to thank Ivana Radosavljeviº Evans
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24 S. Trofimenko, Chem. Rev., 93 (1993) 943.
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